Specific absorption rate (SAR) is an indication of the amount of radiation absorbed by a user of a mobile device. Absorption levels may be typically defined and measured by placing a liquid-filled phantom head, hand, or other emulated body part close to the edge(s) of a mobile device while transmitting. Measurements of a rise in the liquid's temperature provide an indication of the radiation exposure.
Meeting SAR requirements for mobile phones may be addressed by radiation pattern shaping, which is facilitated by the fixed orientation relationship between the mobile phone's handset and the user's head (i.e., next to the ear). However, there are mobile devices that experience variable orientation relationships with the human body, for example cellular modems. A cellular modem may be packaged as a dongle and can be inserted into a portable computer at many different orientations based on the configuration of the portable computer's ports—typically there may be a minimum of four orientations.
To meet SAR requirements, dongles may be designed so as not to exceed predefined SAR limitations in all of its possible orientations. Because mobile antenna patterns may be hard to control, the conventional approach may be to set the antenna radiation limits based on peak radiation points rather than peak radiated averages (i.e., total radiated power (TRP)). This conventional approach may cause vendors to limit the maximum power, the maximum data rate, and/or the minimal physical size of the dongle.